Uniform corrosion anode and method of making same



Patented Dec. 26, 1933 UNIFORM CORROSION ANODE AND METHOD OF MAKING SAMEGeorge Fellmeth Geiger,

signor to The Inc., New York, N. Y.,

Huntington, W. Va., 218- International Nickel Company,

a corporation of Dela- No Drawing. Application March 12, 1930 Serial No.435,356

10 Claims. (01. 204-14 This invention relates to improved anodes em--ployed in the electro-deposition of metals, particularly nickel anodesfor the electro-deposition of nickel.

In particular the invention pertains to a novel nickel anode of the castor rolled type by which more uniform corrodibility with'a smooth surfaceand an increased solubility are obtained than has heretofore beenpossible.

Such adsilicon.

In the use of these improved anodes several advantages, not heretoforeknown, have developed. These advantages are: the producing of muchsmoother plating work; that there is uniform corrosion in a largermajority ofbaths,

which condition has not been possible with other anodes available today;that the anodes are more readily soluble; that it is possible to nowmaintain uniform conditions in the electro-plating bath by reason of thefact that the anodes do not dissolve too easily or not too difiicultly;that the improved anodes corrode in a manner with a smooth surfacethereby substantially eliminating droppings and the presence of slimes.

The invention should not be limited" to the production of anodes alone,as the improved alloy has other advantageous uses, such as theproduction of special cast or rolled products.

Acknowledgment is made of the improvements in carbon-free nickel byMerica and Kayes, ap-

plication Serial No. 192,782, and improvements in Rolled carbon-freeanodes by mudge,- Serial The present improvement gives beneficialresults over the disclosures in those applications.

In plating work, especially in nickel-plating,

one of the main desires has been to obtain smooth anodes which haveshown the best results heretofore have been known as oxygen-bearing ordepolarized anodes.

The most preferred form of that type was a. rolled anode. The castoxygen-bearing anodes were not as satisfactory as the rolled anode ofthat type.

Again, in the plating work, without good control of plating solutionsand unless a very satisfactory anode is employed, rough plating results.

It appears that the greatest trouble of platers today is in obtainingsound and smooth plating. Rough plating is produced when bad anodes areemployed, and usually results from small particles of nickel, orimpurities, being carried from the anode to the work and attachingthemselves thereto as solid bodies, and thereafter building themselvesup in size. This building up is natural as the tops or summits of theseparticles are nearer to the anodes and the current will normally pass tothese high spots and not readily to the valleys between the particles.It will therefore be seen that the resulting plating presents a seriesof hills and dales or valleys in its surface.

It is usual after the plating to brighten same by buffing. It has beenfound during the bufiing process that these particles or hills arepulled out leaving holes in the plating thereby exposing the base metal.The exposure of this metal permits of rusting or corroding to startimmediately. With such bad plating results, the nickel platingdoes notserve its intended purpose, i. e., protecting the metal.

It will therefore be seen that it is highly desirable to obtain and useimproved anodes which have uniform corrosion and which practicallyeliminate particles of nickel in the bath and which permit theproduction of smooth and satisfactory plating in a quick and efiicientmanner.

The improved anodes herein to be described have been found by experienceto give the desired uniform corrosion; to have less sludge on themselvesor in suspension or in the bottom of the bath; to substantiallyeliminate the finding of nickel particles in the bottom of the bath; togive material increase in solubility; and to corrode with a smoothsurface.

Considering these advantages more in general in order to appreciate thereasons therefor, it is found that the advantage of uniform corrosionresides in the fact that substantially all of the nickel in the anode isused for its intended purpose-i. e., plating.

With the improved anode herein very much less sludge is produced, infact, substantially none. when the term sludge" is employed it usuallyrefers to some sort of insoluble material. Whatever very small amountmay manifest itself, it no is not detrimental. It may be found on theanode, or suspended in solution, or in the bottom of the bath.

By the statement that there are substantially no nickel particles in thebottom of the bath, it is meant that the improved anode corrodes withsuch uniformity that the rate of eating or corrosion of the grainsthemselves is substantially the same as the rate of eating of thematerial in the grain boundaries. When particles of nickel are found inthe bath, it means that the material be-,

tween the grains, or within the grain boundaries, as it is often called,is eaten away at a much faster rate than the grains themselves and thegrains fall from the anode before being eaten or dissolved. ,The fallingof such grains means that they either drop to the bottom of the bath andare completely lost for plating purposes, or are held in suspension andcarried to the surface of the member being plated with the attendantunsatisfactory hill and dale plating results above indicated. It mayalso be noted at this point that the eating and corroding within thegrain boundaries may be and often is suificiently fast to eat aroundseveral grains held together. In such an event a whole lump of nickelfalls from the anode to the bottom of the bath and is lost for platingpurposes.

In the improved anode it has been found by microscopic examination of apartially corroded anode that there is substantially no faster eating ofthe material in the grain boundary than in the grains themselves.

The improved anode permits of very materially increased solubility whichmeans less demand of electrical power to transfer the nickel from theanode into solution, and when it is understood that a large number ofthese anodes are employed, the saving in the total electrical energy isvery material and important.

The feature of corroding with a smooth surface is also important. Whenit is possible to obtain an anode'that corrodes with a smooth surface,it is found that a lacy structure, found so often in other anodes, iseliminated. It has been found by investigation that a lacy struc ture ornet work holds sludge and impurities on or at the surface of the anodeand acts as an insulator to the action of corrosion, thereby preventinga ready transfer of the nickel into the bath. In any event theefliciency of plating is very materially reduced when the lacy structureis present. The use of the word corrosion herein is usually employed todenote the action of transferring the nickel into the solution.

From another viewpoint, the impurities permit the starting up of localactions, which create depressions and the formation of the net work.This net work is particularly disadvantageous as it holds sludge andthereby prevents the nickel from being readily transferred into thebath. As the corrosion proceeds, portions of the net work separate fromthe anode in particle or lump formation. While the foregoing may be asatisfactory theory of what happens, it is to be understood that it isonly the most likely definition. In any event, practice and theinvestigations show that when some sort of lace or net work is present,rough plating results.

It'has been found with the use of the improved anode herein that most ofthe caution required in maintaining the bath at a definite workablecondition or neutrality, is substantially eliminated. .With thisadvantage a less skilled at- 'tendant may be employed in the platingwork.

It is believed that the reason for this advantage is that subsiantiallyall of the electrical energy employed is consumed for its desiredpurpose, i. e., transferring the nickel into the solution or bath.

It has been found that the improved nickel anode which has given thesatisfactory results and advantages as above outlined, may be read- 7ily produced, in substantially any physical form of anode heretoforeknown, by adding thereto a material or materials which may readily bedispersed throughout the grains of the nickel and throughout theintergranular material. Such advantageously added materials are found tobe preferably oxygen, with sulphur or similar material in regulatedamounts, the sulphur content preferably ranging between .002 and .020per cent. In some types of anodes just sulphur, or its equivalent indesired amounts is added to give the improved results.

It has been found preferable, however, 'to employ a lower amount ofsulphur in order to reduce the brittleness of the product. For apreferred commercial form and commercial production it is desirable tohave the sulphur within a range of .002 and .005 percent, although arange of 0.0035 to 0.0075 per cent of sulphur gives eminently desirableresults in practice.

It is believed that the added material or materials are dispersedsubstantially uniformly throughout the grains and throughout thematerialin the grain boundaries. This may or may not be the actual fact, but inany event the addition of the materials described above produces verybeneficial and improved results. The examination of the productsmicroscopically shows what is believed to be uniform distribution.

While the presence of some sulphur has been heretofore known, it hasalways been indicated that it is undesirable from the standpoint of hotworking and should be eliminated. It has now been found, especially foranodes and other products, that the presence of sulphur, in controlledamounts, will still permit good hot forging and rolling, and will give,in addition, in plating work, great improvement in the plating, and inthe efiiciency of operation.

Thus, by controlling the addition of the sulphur in various types ofanodes, it has been found that a very material increase in efficiency,in the uniformity of corrosion, and smooth satisfactory plating havebeen obtained without completely sacrificing hot rolling properties.

It has also been found that by controlling the amount of sulphur withinpreferred limits, and

this in anodes of the oxidized, cast or rolled type,

the advantages above outlined are noted to a very marked degree. In anyevent these oxidized, cast or rolled anodes which have sulphur added tothem in controlled amounts, are materially better than such anodeswithout the sulphur.

The nickel oxidized anodes which have nickel oxide added to them within.02 to .25 percent, have been found to give very beneficial results withsulphur present between .002 and .020 percent. The preferred percentagesin an anode which has very satisfactorily shown the improved results,were oxygen .I0-.20,per cent, and sulphur .002.005 percent. Otherpreferred percentages I of sulphur in anodes which have given verysatisfactory use range between 0.0035% and 0.0075%,

with the average preferred amount being 0.005%.

While the preferred disclosure illustrates the advantages of theaddition of oxygen and sulphur within satisfactory ranges, it is to beunderstood that other materials may be employed for 010- tainingsubstantially the same results in produc ing a satisfactory anode whichwill give uniform corrosion and most of the other advantages aboveoutlined. Thus, it will be seen that certain ele ments or compounds maybe substituted for the sulphur. Desirable elements or compounds orequivalents for the sulphur have been found to be manganese and silicon,the former being employed in about .10-.25 percent, and the latter inabout .l0-.30 percent. It was also found that the oxygen content whenadding these elements, could be varied from .02 to .25 percent. Asatisfactory balance between the quantities of sulphur or itsequivalents on the one hand, and the oxygen on the other, may be made. 7

In producing the improved anodes herein, it is usual to proceed asfollows: The nickel employed is first melted down, then a desirableamount of sulphur or its equivalent is added in order to obtainsubstantially uniform distribution thereof throughout the mass, the bathis then fiapped, or treated as by adding nickel-oxide or in anydesirable manner 'to give the desired oxygen content. The melt is thentapped and poured into ingot form, and afterwards forged and rolled toan anode or other form. The anodes mayor may not thereafter be submergedin an alcohol-water bath to reduce any oxide coating which may bepresent on the metal.

In the manufacture of substantially all types of anodes, including heattreated anodes, there has been found to be formed thereon a relativelythin coating or skin which has been termed passive nickel. In mostinstances it is desirable to remove this coating or skin so that thecorrosion may start immediately upon the introduction of the anode intothe bath.

It has been found with oxygen-bearing and other anodes which have thesulphur content or its equivalent included therein, that once thecoating or skin has been removed, there is no further formation of suchskin, even though the anode may be withdrawn from the bath severaltimes. This is an important advantage not heretofore known or disclosed.

It may be noted that the presence of the skin is very detrimental at thestart of the operation of plating as actual corrosion is very materiallybath is changed or modified, that a new skin forms on the old type ofanodes. It is of particular advantage that there shall not be aformation of skin every time an anode is dried or handled. The improvedanode herein does not have this disadvantage. Thus greater efficiency inthe plating work is accomplished with the improved anodeshereindescribed.

It has been found by experience with anodes that the coating or skin maybe readily removed by subjecting them to corrosion in a 3-5 percentsolution of hydrochloric acid. This is known as a. deskinning operation.The anode may be made more suitable for deskinning by quenching afterhot rolling from a temperature 1700-1800 degrees Fahrenheit in analcohol water solution containing one part alcohol to eighty parts ofwater. The alcohol bath has been found satisfactory for the purposes,but other baths may be employed, if desired.

When the plating bath is readily maintained at its preferred slightacidity of pH5.4 to 6.7 the improved anode herein permits thecontinuance thereof for a much longer period than with the old types ofanodes. In the event of slight changes in the composition of the bath,then the anodes of controlled oxygen and sulphur content, such as aredisclosed herein, will permit the continuance of good uniform corrosionunder these poorer and less desirable bath conditions.

It will be seen from the foregoing that with a controlled amount ofoxygen and/or sulphur, or its equivalent in the anode, an improved anodewill be produced. This effective anode has eliminated many prior platingtroubles, insured smoother and better plating and easier control of thebath. There is consequently greater efficiency of operation, a moreuniform. corrosion and increased solubility. Less sludge is formed andthere are practically no nickel particles in the bottom of the bath.

From microscopic examinations of the improved anodes, it appears thatthe oxygen and/or sulphur, or the materials which act as the lattersequivalent, or the reaction products thereof, are substantiallyuniformly distributed throughoutthe grains and throughout the materialin the grain boundaries.

It will also be seen that the improved article of manufacture comprisesan anode which gives improved electro-deposition through improvedcorrosion, and is of a type that results insubstantially no metallicanode droppings, that gives no a smooth anode surface and substantiallyno anode sludges, all of which are recognized as characteristics of themost eificient functioning anodes.

It is to be understood that various changes 1 5 and modifications may bemade, but that-such changes and modifications are to be considered asbeing within the scope of the invention as outlined in the followingclaims.

What is claimed is: I

1. An article of manufacture comprising a rolled or cast nickel anodewhich corrodes with a smooth surface and with substantially no anodesludges, said anode having therein oxygen and a regulated sulphurcontent between .002 and .0075 125 percent sulphur.

2. An article of manufacture comprising a. rolled or cast nickel anodewhich corrodes with a smooth surface and with substantially no anodesludges, said anode having therein a regulated 130 sulphur contentbetween .002 and .0075 percent sulphur.

3. As an article of manufacture, a rolled or cast nickel anode havingsulphur substantially uniformly distributed throughout the grains andgrain boundaries thereof, said sulphur being present between .002 and.0075 percent.

4. As an article of manufacture, a rolled or cast nickel anode having asulphur content of substantially .005 percent. 14d

5. As an article of manufacture, a rolled or cast nickel anode having asulphur content of substantially 0.002 to 0.020 per cent.

6. As an article of manufacture, a rolled or cast nickel anode having asulphur content of a substantially 0.005 to 0.0075 per cent.

7.A nickel anode with 0002-0075 per cent sulphur distributedsubstantially uniformly throughout the grains and the material in the150 grain boundaries, and including oxygen between 0.02 and 0.25 percent.

8. A rolled nickel anode with 002-005 percent sulphur distributedsubstantially uniformly throughout the grains and the material in thegrain boundaries, and including oxygen between .02 and .25 per cent.

9. A rolled nickel anode with .005 percent

